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Effects of Substrate Bias on Microstructure of Osmium-Ruthenium Coatings for Porous Tungsten Dispenser Cathodes

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3 Author(s)
Wen-Chung Li ; Dept. of Chem. & Mater. Eng., Univ. of Kentucky, Lexington, KY ; Scott Roberts ; T. John Balk

Osmium-ruthenium (Os-Ru) films used as coatings for porous tungsten (W) dispenser cathodes were investigated in this study. By applying different levels of substrate biasing power during sputtering, the texture of deposited Os-Ru films varied between {0002}, {10-10}, and {10-11} in this hexagonal close-packed alloy. Furthermore, film texture changed from one preferred orientation to other preferred orientation(s) during annealing (at 1050degCB for 10 min), during which the microstructure of certain Os-Ru films changed from a columnar to an equiaxed grain morphology. Due to a low degree of texture transition during annealing and due to the high compositional and structural stability of the Os-Ru grains, a 5 W bias power appears to be best for film deposition. In addition, the 5 W biased Os-Ru films transformed completely into a basal plane texture, which has the highest planar density, and grain size increased significantly (from ~20 to ~100 nm) during annealing, all while maintaining a columnar grain structure. These characteristics are believed to be helpful in inhibiting interdiffusion between the W substrate and the Os-Ru film. Preventing or slowing the interdiffusion of W atoms can improve the lifetime and even the performance of dispenser cathodes.

Published in:

IEEE Transactions on Electron Devices  (Volume:56 ,  Issue: 5 )